Inorganic substances and more specifically, fertilizers, such as ammonium phosphates, calcium phosphates, ammonium nitrates, potassium nitrates, potassium chlorides, potassium sulfates, etc., are widely used. Methods of manufacturing these inorganic materials, as well as methods of processing the materials into particles via prill and granulation techniques, are also known. The resulting particulate materials, however, often exhibit an undesirable level of dust formation and/or caking. When handled or transported, the granular particles can easily break into smaller particles, resulting in a substantial amount of dust. Additionally, granular inorganic particles, such as fertilizers, often tend to cake when stored and transported in bulk, resulting in substantial amounts of the initial free flowing particulates agglomerating into larger solid masses.
Dust emission is a problem creating a growing concern about atmospheric pollution and its possible ecological and toxicological effects. For example, while it is preferable to produce non-dusty fertilizer particles, special antidust treatments are often applied, due to the difficulty in manufacturing useable particulate fertilizer that does not emit dust.
Dust consists of airborne particles the majority of which are about 10 micron size or smaller created during the production and handling of fertilizers and other inorganic particulates. Depending upon the type of substrate, simple remediations like aspiration and water spray may be applied. To reduce the dust on fertilizer, a petroleum residue or hydrogenated mineral oil is typically sprayed onto the fertilizer. The application of the anti-dusting agent occurs generally during the drying of the phosphate granules in the tumbler. This facilitates the complete coverage of the coating onto the fertilizer particle surface.
Until this time, treatment of inorganic particulates, such as fertilizers, has focused on petroleum-based products, mineral oils, and waxes. There are disadvantages involved in such treatment methods. Oils tend to volatilize and/or soak into the fertilizer with time and lose their effectiveness, while waxes and petroleum-based products are difficult to handle, and can require special heated application equipment. Inorganic particulates coated with petroleum-based products can generate residues on handling equipment, and, in the case of coated fertilizers, typically result in the separation of scum upon dissolution of the fertilizer in water. Other dust treatment methods involve application of an aqueous lignosulfonate solution, other liquid fertilizers, or water to the fertilizer particles. While liquid treatment compositions, such as these, may reduce the fertilizer dust levels, the liquid compositions coated on the fertilizer particles tend to promote caking of the granular fertilizer particles.
A number of conditioning agents have been applied to fertilizers during processing in an attempt to harden and implant anti-caking and anti-dusting properties to fertilizer particles. For example, anti-caking properties have been imparted to fertilizer particles by utilizing clay, talc, surfactants, or a combination of these three conditioners, to coat the particles. Additionally, various oils have been sprayed on fertilizer particles for controlling dust. A phosphoric acid-boric acid compound has also been utilized in phosphate production as a hardening agent. Urea and other fertilizers have also been treated with lignosulfonates alone, or in combination with a co-additive, such as molasses.